1. Field of the Invention
The present invention relates to an apparatus for controlling the operation of a fluid pressure raising system including at least a motor and a fluid machine adapted to be driven by the motor, such as a turbocompressor for refrigerator, centrifugal compressor for pressurizing gases, centrifugal blower and the like.
2. Description of the Prior Art
Japanese patent publication No. 21332/74 to Shoji Ichikawa and Japanese patent publication No. 18942 to Shuichi Takada et al. are cited as showing prior art.
Referring first to Japanese patent publication No. 21332/74, there is disclosed a turbo-refrigerator having a turbo-compressor, a motor for driving the compressor, a condenser adapted to condense the refrigerant, and expansion or reducing valve for releasing the pressurized and liquefied refrigerant coming from the condenser, an evaporator adapted to allow the liquefied refrigerant released by the expansion valve to evaporate, suction vanes disposed in the suction-side passage of the compressor and so forth. In this turbo-refrigerator, the motor for driving the compressor is a high-speed D.C. motor or a thyristor motor connected to a D.C. power supply through a speed controller such as a variable resistor or a thyristor chopper. This speed controller is adapted to control the speed of rotation of the impeller of the turbo-compressor in accordance with the temperature differential between the evaporatoroutlet brine temperature and the condenser-inlet cooling water temperature.
The speed control of the turbo-compressor in accordance with the above mentioned temperature differential or the change of the cooling water temperature makes it possible to minimize the required electric input power and, therefore, greatly contribute to save the energy.
The above explained refrigerator, however, requires an uneconomically large equipment for the speed control, because it relies upon a high-speed D.C. motor, D.C. power supply and speed controller constituted by a variable resistor or a thyristor chopper, and a stupendous installation cost. One of the factors for raising the cost resides in the indispensableness of an AC-DC convertor, i.e. a D.C. motor generator, for converting the commercially available A.C. power to D.C. power.
Referring now to Japanese patent publication No. 18942/77, there is disclosed a turbo-refrigerator having a turbo-compressor, a prime mover for driving the turbo-compressor, a condenser adapted to condense the refrigerant compressed by the turbo-compressor, and a cooler for cooling the refrigerant flowing into the compressor. The speed of the prime mover is adjusted by a governor which is adapted to be controlled in accordance with the flow rate of cooling fluid for cooling the condenser or the pressure of the refrigerant in the condenser which is detected by a specific detector. This turbo-refrigerator can ensure the same advantageous effect as that provided by the refrigerator of the firstmentioned Japanese patent publication No. 21332/74.
The prime mover of this refrigerator for driving the turbo-compressor is a steam turbine, highfrequency electric motor or the like. However, the increment of the size and cost of the controlling equipment cannot be avoided whichever may be used as the prime mover. At the same time, the use of a steam turbine, which inherently has a low efficiency, inconveniently lowers the efficiency of the refrigerator as a whole and demonstrates the need for increasing the efficiency of the turbo-compressor as, for example, by improvement in the speed control.
Thus, the prior art poses new problems to be solved: to simplify the construction of the speedcontrolling equipment and to lower the costs of manufacture and installation.